Re: [PATCH 4/8] drm/panthor: Add support for protected memory allocation in panthor

[Chia-I Wu <olvaffe@gmail.com>]

On Tue, May 12, 2026 at 8:39 AM Liviu Dudau <liviu.dudau@arm.com> wrote:
>
> On Tue, May 12, 2026 at 04:11:11PM +0200, Boris Brezillon wrote:
> > On Tue, 12 May 2026 14:47:27 +0100
> > Liviu Dudau <liviu.dudau@arm.com> wrote:
> >
> > > On Thu, May 07, 2026 at 01:53:56PM +0200, Boris Brezillon wrote:
> > > > On Thu, 7 May 2026 11:02:26 +0200
> > > > Marcin Ślusarz <marcin.slusarz@arm.com> wrote:
> > > >
> > > > > On Tue, May 05, 2026 at 06:15:23PM +0200, Boris Brezillon wrote:
> > > > > > > @@ -277,9 +286,21 @@ int panthor_device_init(struct panthor_device *ptdev)
> > > > > > >                     return ret;
> > > > > > >     }
> > > > > > >
> > > > > > > +   /* If a protected heap name is specified but not found, defer the probe until created */
> > > > > > > +   if (protected_heap_name && strlen(protected_heap_name)) {
> > > > > >
> > > > > > Do we really need this strlen() > 0? Won't dma_heap_find() fail is the
> > > > > > name is "" already?
> > > > >
> > > > > If dma_heap_find() will fail, then the whole probe with fail too.
> > > > > This check prevents that.
> > > >
> > > > Yeah, that's also a questionable design choice. I mean, we can
> > > > currently probe and boot the FW even though we never setup the
> > > > protected FW sections, so why should we defer the probe here? Can't we
> > > > just retry the next time a group with the protected bit is created and
> > > > fail if we can find a protected heap?
> > >
> > > The problem we have with the current firmware is that it does a number of setup steps at "boot"
> > > time only. One of the steps is preparing its internal structures for when it enters protected
> > > mode and it stores them in the buffer passed in at firmware loading. We cannot later run the
> > > process when we have a group with protected mode set.
> >
> > No, but we can force a full/slow reset and have that thing
> > re-initialized, can't we? I mean, that's basically what we do when a
> > fast reset fails: we re-initialize all the sections and reset again, at
> > which point the FW should start from a fresh state, and be able to
> > properly initialize the protected-related stuff if protected sections
> > are populated. Am I missing something?
>
> Right, we can do that. For some reason I keep associating the reset with the
> error handling and not with "normal" operations.
I kind of hope we end up with either

 - panthor knows the exact heap to use and fails with EPROBE_DEFER if
the heap is missing, or
 - panthor gets a dma-buf from userspace and does the full reset
   - userspace also needs to provide a dma-buf for each protected
group for the suspend buffer

than something in-between. The latter is more ad-hoc and basically
kicks the issue to the userspace.

For the former, expressing the relation in DT seems to be the best,
but only if possible :-). Otherwise, a kconfig option (instead of
module param) should be easier to work with.

Looking at the userspace implementation, can we also have an panthor
ioctl to return the heap to userspace? A dma-heap ioctl to query the
heap size is also lacking.


>
> Best regards,
> Liviu
>
>
> --
> ====================
> | I would like to |
> | fix the world,  |
> | but they're not |
> | giving me the   |
>  \ source code!  /
>   ---------------
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>